Your campaign has been sent, but some customers find it in spam and others never receive it. The cause may be domain settings, the source of your list, complaints, sending volume or the email itself. Changing the subject line without checking the other factors rarely explains the problem.
Start by identifying which emails are affected, at which mailbox providers and after which change. Then address confirmed causes and monitor the outcome.
First, establish what is happening
Distinguish between three situations:
- The email was rejected. The report shows a delivery error. You need the receiving server’s response code and explanation.
- The server accepted the email, but it landed in spam. A delivery status in your email platform does not confirm inbox placement.
- The email arrived, but the recipient did not notice or open it. This alone is not evidence of a delivery problem.
Check whether the whole list or only certain domains are affected, and whether the issue concerns one campaign or all messages. Compare the situation before and after changing your platform or sender address, importing contacts or increasing frequency.
Do not draw conclusions from a single test mailbox. Collect feedback from recipients, sample emails with their headers and delivery error reports.
Check domain authentication
SPF, DKIM and DMARC help the receiving service verify where an email came from.
The basics are explained in Mailchimp’s guide to SPF, DKIM and DMARC.
Senders of more than 5,000 messages a day to personal Gmail addresses must use SPF, DKIM and DMARC; all senders need at least SPF or DKIM. Google recommends setting up all three. Also check secure transmission and DNS requirements in the Gmail sender guidelines.
Check not only that DNS records exist, but also the authentication results of an actual email. Your website, CRM, business email and campaign platform may send messages in different ways.
Use the record values provided by your own provider. Do not copy another company’s settings or remove existing records without checking: this could affect other business emails. Successful authentication alone does not guarantee inbox placement.
Review the source and condition of your list
Each segment should have a clear origin: where and when people subscribed, which messages they expected and whether they have opted out.
Check:
- whether new subscribers have been mixed with an old list of unknown origin;
- whether unsubscribed recipients and people who complained are excluded;
- how invalid addresses and permanent delivery failures are handled;
- whether a new import puts suppressed contacts back into campaigns;
- whether the content matches what was promised at signup.
Verifying that an address exists does not confirm permission to send marketing emails. Purchased lists or contacts found online do not become subscribers simply because their addresses work.
If the source of part of the list is unclear, keep it out of general campaigns until its permitted use has been established. Do not send a mass “confirm your subscription” message to recipients where even that communication lacks a valid basis.
Check complaints and unsubscribing
A visible unsubscribe option lets people stop unwanted messages. A hidden link, a broken page or another campaign after opting out leaves the problem unresolved.
For bulk senders, Yahoo requires an easy unsubscribe mechanism through the List-Unsubscribe header and a visible link in the message body. A footer link alone does not replace the technical mechanism. See Yahoo’s sender requirements.
Test unsubscribing with a test contact: does their status change, do marketing flows stop, and does the exclusion remain after syncing with the CRM?
Keep marketing campaigns separate from essential notifications about an existing order. They need distinct workflows and sending rules.
Review frequency and changes in volume
If someone subscribed to useful content but now receives several offers every day, expectations and frequency may be the issue. Count messages from all campaigns and automated flows together.
Pay particular attention after a long pause or a sharp increase in volume. Start with a segment whose subscription and current interest are clear, and monitor errors and recipient responses.
Do not try to solve the problem by repeatedly changing domains. A new address will not fix the source of the list or the communication itself.
Check the email content
Recipients should recognise the company and understand why they received the message. Check the sender name, subject, reply address, links and whether the offer suits the segment.
Avoid misleading subjects, artificial “Re:” prefixes, false urgency and unclear links. Make sure the email is readable on a phone and its main message makes sense even when images do not load.
There is no universal list of words whose removal guarantees delivery. Filters consider multiple signals, as explained in Mailchimp’s guidance on spam filters.
How to prioritise checks
What to monitor after making changes
Record delivery errors, complaints, unsubscribes, authentication results and how issues vary by mailbox provider. For Gmail, use the available Postmaster Tools data. A low open rate alone does not confirm spam placement: Google specifically explains the limitations of this metric in its sender guidelines.
Log the date, affected segment, change and result. Do not increase sending volume just because one test email reached the inbox.
You can discuss list checks, technical settings and workflows as part of our email marketing service. The scope of setup and ongoing management is described in our commercial proposal.